Today, it is utilized in quite various fields to make a robot grasp an object and perform any working operation, e.g. grasping and transporting parts on the auto product assembling line in the factory, and transporting/controlling inventories in the automated warehouse. There are examples in the limitless number.
For such an industrial robot, one of the important technologies sought for grasping lies in an art for placing the grasp force under control in order to prevent the object being grasped from falling down. For example, JP-A-4-189484 describes a structure having an end effecter provided, at its finger end, with a sensor for detecting a slide of the grasped object wherein, when a slide of the object of grasping is detected by the sensor, finger grasp force is increased a predetermined amount by a grasp-force control apparatus, thereby enabling to positively grasp the grasped object without falling by a minimum grasp force.
The prior-art grasp control technologies as in the above are mainly for industrial applications. These are the arts necessitated for correctly performing the operations to grasp and move an object and then release it, in accordance with a previously determined program.
Meanwhile, recently, humanoid-type robots have been developed vigorously toward the goal of assisting human life while coexisting with mankind. The humanoid-type robot has one of the major developmental objects to explore the possibility of coexistence with mankind. This is one of the significant differences from the traditional industrial robots.
The coexistence with mankind inevitably requires the realization of interaction with a person. This necessitates the functions to be realized in a hardware fashion in addition to the functions realizable on software, such as personal recognition and speech dialogue. The hardware-like interaction function includes those of functions to shake hands and exchange a grasped object with a person.
However, there is a difficulty in applying, as an example of robot-human interaction, the technology described in JP-A-4-189484 to the grasp-force control of an end effecter for delivering an object being grasped by the robot over to a person. This is because, in case the person is to take out an object being grasped by the robot, the robot is controlled toward the stronger grasping not to be deprived of the grasped object. Accordingly, in some cases, there are possibly problems of breaking the grasped object.
Meanwhile, the conventional humanoid-type has the function to grasp an object. However, concerning the function of delivering a grasped object from the robot over to the person, there has been realized nothing more than a quite simple method not requiring real-time control of grasp-force. For example, adopted is a method that an end effecter imitating the human hand turns its palm up, and the grasp is released so that a grasped object is placed on the palm, allowing a person to take it up, making a state in which the grasped object can be taken up anytime. Thus, there is no hardware-like interaction function with a person.